Coated member and method of making the same



M. s. ROUSH Aug. 17,1934

COATED MEMBER AND METHOD OF MAKING THE SAME Filed Oct. 19, 1948 5 E V Z1% H Patented Aug. 17, 1954 UNITED STATES OFFICE COATED MEMBER ANDMETHOD OF MAKING THE SAME Milton S. Roush, Painesville, Ohio, assignorto Thompson Products, Inc., Cleveland, Ohio, a

corporation of Ohio 9 Claims.

The present invention relates to the coating of metal surfaces withprotective organosiloxane films and to members having such a surface.More particularly, this invention deals with the organosiloxane coatingof metals which do not normally retain such coating wherein thenonadherent metal is provided with an intermediate layer of a metal towhich organosiloxane films adhere tenaciously.

The organosiloxane polymers, commonly known as the silicones, are longchain or cyclic organosilicon compositions in which organic groups areconnected by carbon-silicon bonds to the silicon atoms of asilicon-oxygen network. The high molecular weight organosiloxanepolymers are conventionally prepared by the hydrolysis and subsequentcondensation of the corresponding organosiloxane halides or esters. Thepreparation of organosilicon halides and the hydrolysis and condensationof the halides to form the organosiloxane may, for example, be carriedout in the manner described in United States Letters Patent No.2,258,218 to Eugene G. Rochow.

Resins for coating metallic and other surfaces may be prepared by theco-hydrolysis and cocondensa-tion in a suitable hydrocarbon solvent of amixture of organosilicon halides containing differing organicconstituents. For example, a suitable coating resin may containdimethylsiloxane units, monomethylsiloxane units, andphenylmethylsiloxane units. The specific physical and chemicalproperties of the resin are dependent upon the proportions ofingredients and the degree of condensation of the copolymer.

I have found that closely adherent, smooth coatings capable ofwithstanding elevated temperatures may be obtained by the application oforganosiloxane resin to surfaces of metals capable of forming adherentmetal oxides, such as magnesium and aluminum. Such metals arehereinafter referred to as receptive metals. Upon heating theorganosiloxane resin-coated surface to a temperature on the order offrom 230 to 320 C., the interfacial layer between the metal and theresin assumes the color of the metal oxide and it appears that the metaloxides tightly bond the coating to the metal surface through metaloxygenlinkages within the polymer. However, in the case of metals incapable offorming adherent metal oxides, the siloxane film is not tightly bondedto the metal surface, the film flakes and cracks at elevatedtemperatures, and the metal surface is said to be non-receptive.

The organosiloxane film coatings have been found to be particularlydesirable for coating fluid flow directing receptive surfaces suitablefor use in turbine engines due to the non-wettability of the film, thesmoothness, and the corrosion and erosion resistance of the siloxanelayer. Since fiow directing members formed of receptive metals must bemanufactured by costly and complicated forging methods, it has beenproposed that such members and particularly the air directing blades ofthe engine be fabricated from porous iron compacts formed to shape bypowdered metal methods and infiltrated With copper to form a dense bodystructure. Due to the non-receptive character of both iron and copper,it has heretofore been impossible to coat such blades with a protectiveorganosiloxane film.

The present invention now provides a method whereby an organosiloxaneprotective film may be applied to an article formed of a metal incapableof forming an adherent metal oxide. In accordance with the method of thepresent invention, the non-receptive metal surface is coated, as byelectrodeposition or dipping, with a receptive metal. A layer of anorganosiloxane polymer, preferably dispersed in a liquid medium, is thenapplied to the receptive metal surface, the polymer being subsequentlycured and condensed by heating to form a continuous film tightly bondedto the non-receptive base metal by the receptive layer and the receptivemetal.

As particularly applied to the coating of fluid flow directing membersformed of a porous iron compact infiltrated with copper, the method ofthe present invention comprises the steps of etching copper from thesurface and adjacent top surface layers of the infiltrated compact,forming a deposit of a receptive metal, such as cadmium, tin, zinc oraluminum, on the exposed iron surfaces, applying under reduced pressurea layer of an organosiloxane polymer to the exposed etched surfaces ofthe compact and to the receptive metal surface, and heating the siloxanecoated member to cure the siloxane resin and to react the resin with thereceptive metal surface. If desired, prior to curing the initialorganosiloxane layer applied to the receptive metal surface, anadditional organosiloxane layer may be applied to the article to providean additional siloxane thickness presenting a smooth surface. The coatedmember thus provided comprises a body or base composed of non-receptivemetal, a receptive metal layer deposited on the non-receptive surface,and an organosiloxane layer overlying the receptive metal surface, theorganosiloxane polymer extending into the etched surface layers of thenonreceptive surface and being firmly bonded to the receptive metalsurface by an interfacial layer of receptive metal oxide.

It is, therefore, an important object of the present invention toprovide a method for the application of adherent organosiloxane film toa metal article formed of a non-receptive metal.

It is another important object of the present invention to provide amethod for firmly bonding an organosiloxane polymer to a non-receptivemetal article by means of an interfacial layer of a receptive metal.

It is a further important object of the present invention to protectnon-receptive metal surfaces with an organosiloxane polymer by applyinga layer of a receptive metal to the non-receptive metal article,subsequently coating the receptive metal layer with an organosiloxanepolymer and heating the coated surface to cure the polymer and to effecta reaction between the polymer and the receptive metal.

Another object of this invention is to provide an organosiloxane coatedmetal article in which the organosiloxane polymer is bonded to thearticle b means of an intermediate layer of a receptive metal depositedon the surface of the article and firmly bonded to the polymer by meansof receptive metal-oxygen linkages within the polymer.

It is a still further important object of the present invention toprovide a fluid flow directing member formed of a non-receptive metalenveloped within a protective org-anosiloxane film, the polymer beingbonded to the fluid directing member by means of an intermediate layerof a metal capable of forming a tightly adherent metal oxide.

A specific object of the present invention is to provide a method forthe coating of an air flow directing blade made of a porous iron compactand infiltrated with copper by etching copper from the blade surface,depositing a receptive metal selected from the group consisting ofcadmium, tin, zinc and aluminum on the exposed iron blade surface,depositing a layer of organosiloxane polymer on the receptive metalsurface, and heating the coated blade to bond the polymer to thereceptive metal surface.

Other and further objects of this invention will be apparent from thedisclosures in the specification and the accompanying drawings.

On the drawings:

Figure 1 is a perspective view illustrating a compressor blade such asthat employed in a turbojet engine;

Figure 2 is a greatly magnified fragmentary view illustrating thestructure of a copper infiltrated iron compact, such as the blade ofFigure 1;

Figure 3 is a view similar to Figure 2 illustrating the structure of thecompact following etch- 1 Figure 4 is a view similar to Figure 3illustrating the structure of the etched compact following thedeposition of a receptive metal thereon;

Figure 5 is a view similar to Figure 4.- illustrating the structure ofthe compact of Figure 4 following the deposition of an organic siloxanepolymer thereon under reduced pressure; and

Figure 6 is a view similar to Figure 5 illustrating the structurefollowing the application and curing of the outer organcsiloxane layer.

As shown on the drawings:

In Figure 1, reference numeral It refers generally to an airflowdirecting blade suitable for use in a turbo-jet engine. The blade l0comprises an airfoil vane section II and a root 12 for anchoring theblade in position in a turbo-jet engine compressor rotor or stator. Theairfoil portion H has a concave face Ma and a convex face i ll)appropriately shaped to effectively pack air into the engine. Inaddition, the airfoil portion ii is twisted along its length, the facesIla and i lb and the twist presenting a contour that is very difiicultto manufacture and which heretofore could only be made by costly forgingand machining operations followed by extensive polishing.

While satisfactory blades it can be made by powder metallurgy technique,it is also necessary to provide highly polished exterior surfaces on thevane faces 1 la and 1 lb. By practicing the method herein disclosed, itis possible to readily and inexpensively manufacture blades havinghighly polished airfoil surfaces.

One particularly desirable method of inexpensively forming the blade 10includes a combined powder metallurgy and infiltration technique whereinpowdered iron is pressed to form a porous compact which may be sinteredif desired. The compact is subsequently infiltrated with copper. Such aninfiltered compact may be prepared by pressing to blade shape powderediron, preferably free of carbon but, if desired, containing up to 1%carbon, at pressures ranging from 6 to 50 tons per square inch. If ironpowder of suitable particle size, ranging from 80 to 325 mesh, isemployed, a compact having a porosity ranging from 10 to 35% will beproduced at these pressures. If the porosity of the compact is greaterthan 15%, it is desirable to sinter the compact at a temperature of 900to 1100 C. for a period of from 30 minutes to 1 hour. If necessary, theporosity of the compact may be reduced to less than 15% by coining.

Following the formation of the porous iron compact, the compact isinfiltrated with copper or a copper alloy to produce the desired densebody structure by contacting the porous shape with copper and heating ina dry protective atmosphere to a temperature greater than the meltingpoint of copper or the copper alloy being employed. This heating maysuitably be carried out by temperatures ranging from 1125 to 1150 C. fora period of from 10 to 15 minutes. While pure copper may be used forinfiltrating, it is preferred to use a copper base alloy containing 2%to 8% manganese and 1% to 2% iron.

If desired, the infiltrated body may be subjected to suitable heattreatments, such as diffusion and precipitation or steel treatments, tosuperficially alloy the ferrous skeleton and copper network bydiffusion. The dense body structure thus obtained is illustrated inFigure 2, in which reference numeral l3 designates the compacted ironparticles and reference numeral ill indicates the copper infiltranttherebetween.

In accordance with the method of the present invention, the infiltratedcompact is etched, either electrolytically or chemically, to removecopper from the compact surface and adjacent layers to a depth rangingfrom approximately 0.002 to 0.01 inch. This etching may be desirablycarried out by means of a combined chromic acid-sulphuric acid etchingsolution. A suitable solution, containing about 187.5 grams per liter ofchromic acid and 1.88 grams per liter of sulphuric acid, may be preparedby diluting with water a dilute commercial chromium plating bath to acidstrength. As shown in Figure 3, this etching step results in theformation of a porous surface free of copper and presenting ironparticles spaced at random at their etched surface.

Inasmuch as organosiloxane polymers do not adhere to either copper oriron at relatively elevated temperatures, it is desirable to provide areceptive metal surface overlying the iron surface of the metal compactto which the organosiloxane polymer may adhere. As shown in Figure 4,the provision of a receptive metal surface is carried out by depositinga receptive metal [5 onto the exposed iron particles constituting thearticle surface. Suitable receptive metals which may be easily appliedto the iron surface are cadmium, zinc, tin and aluminum. A cadmium,zinc, or tin layer may suitably be deposited by conventionalelectroplating procedures or dipping, while I prefer to deposit aluminumby means of a hot aluminum dip process. Any receptive metal capable offorming an adherent metal oxide may be employed to anchor the polymer tothe blade formed of non-receptive metal. However, the above named metalsare preferred, due to their ease of application and the extremelyadherent bond formed between these metals and organosiloxane polymers.

As shown in Figure 4, the receptive metal will be deposited on theexposed iron surfaces and will follow the outline of the exposed edgesof these particles. If the grains of iron are closely spaced, as at I 6,the receptive metal layer l5 will seal off the etched portion lyingbeneath the iron particles to leave a void. However, a majority of theseopenings will not be closed, and access to the underlying copperfiltrant l4 will be provided by the etched cavities.

Following the deposition of the receptive metal layer [5 upon thesurface of the article, the article is next heated to a temperature ofgreater than 100 C. and preferably 150 C. to dry the article surface.Following this heating step, the article, while still hot, is placedwithin a conventional vacuum chamber which is evacuated at a pressure ofless than 1 mm. mercury to remove moisture from the article and toevacuate air from the surface pores formed by the etching step. Whilemaintaining the article under vacuum, the article is contacted withsuitable organosiloxane resin. For example, an organosiloxane resincontaining dimethylsiloxane, monomethylsiloxane, andphenylmethylsiloxane structural units may be employed. Resins of thistype are manufactured by Dow Corning Corporation under the trade nameDC804. The resin employed in this step is preferably diluted to a solidcontent of dispersed in suitable hydrocarbon solvent, such as toluene.

As illustrated in Figure 5, the silicone resin I! may be deposited uponthe receptive metal surface l5 and also deposited within the etchedpores underlying the iron particles l3 forming the article surface. Thispenetration of the siloxane polymer dispersion is made possible by theevacuated condition of the etched pores and the free flowingcharacteristics of the 15% solids dispersion. As shown in Figure 5, thesilicone forms films l1 following the contour of the metal l5 anduniformly distributed over the exposed receptive metal surfaces andlining the etched pores of the metal article.

Following the formation of siloxane layer H, the vacuum is released andthe coated article is removed from the vacuum chamber. Following thiscoating, the siloxane coated article may be cured as hereinafterdescribed, but I prefer to apply a thicker organosiloxane coating, asillustrated at l8 in Figure 6, to provide a smoother coating. Theapplication of the later coating is accomplished without curing thefirst siloxane coating l7, since I have found that the applica tion andcuring of a second layer to a cured condensed initial polymer layer willcause crazing upon drying and exposure to elevated temperatures. Iprefer to dip in a suitable solvent, such as toluene, the coatedarticle, as shown in Figure 5, to remove the silicone coating from thesurface of the receptive metal layer l5. This dip does not remove thesilicone layer lining the Walls of the etched pores since the extremelysmall dimensions of these pores prevents the penetration of the solvent.

Following the toluene dip, the article surface is preferably sprayed orotherwise coated with a siloxane resin of the same composition as thelayer ll, although if desired a different resin composition may beemployed. I prefer to employ a more concentrated dispersion of siloxanefor the later coating 18, preferably a dispersion containing from 30% to60% resin solids. The completed coating [8 should be less than 0.004inch thick and preferably on the order of 0.001 inch thick.

I have found that coatings of greater thickness than 0.004 inch crazeupon subjection to elevated temperatures and that a coating less than0.001 inch thick becomes porous and less solvent and corrosionresistant. It is to be noted in Figure 6 that the coating 18' penetratesand fills the etched cavities outlined by the preliminary layer Hi. Thisfilling of the etched pores is possible because of the substantiallyidentical composition of the two coatings dissolved in the same solventso that the preliminary coating is wet by the compatible coating laterapplied.

Following the application of the layer H, the coated article ispreferably air dried for a period of time sufficient to substantiallyremove the hydrocarbon solvent from the coating. If desired, this airdrying step may be carried out at an elevated temperature, although Iprefer to air dry the coated article at room temperature for a period ofapproximately three hours. Following this air drying step, a coatedarticle is subjected to baking in a substantially solvent freecondition, thus avoiding bubbling, blisters, etc.

After the air drying, the coated article is pref erably subjected to apreliminary baking for a period of about 1 hour at a temperature of fromto 200 C., and preferably at a temperature of approximately C. Thepreliminary baking effects a partial fusion of the polyorganosiloxanepolymer to give a more compact coating and prevents the damaging of thecoating upon suddenly subjecting the coated article at room temperatureto the relatively high baking temperatures subsequently employed.

In general, it is desirable to bake the coating at a temperature abovethe highest temperature to be encountered in operation of the article.In a multi-stage axial flow air compressor operating at a compressionratio of 5 to 1, as in turbo-jet engines, the highest temperature towhich any of the blades in the compressor will be subjected isapproximately 254 C. plus the temperature of the incoming air. I havefound, however, that curing at a temperature of about 260 C. isgenerally sufficient, since following curing at this temperature thecoating will not become tacky, even upon severe heating at greatlyelevated temperature. The minimum temperature at which the improvedcoating of the present invention may be obtained is approximately 230 C.and a maximum temperature which I prefer to employ is approximately 320C. The baking temperature should be maintained for a period of about 6to 12 hours for optimum results.

I have found that the advantages residing in the coating of an airdirecting member with an organosiloxane by the method of the presentinvention are three-fold. First, such a member coated with anorganosiloxane as herein defined possesses an improved, smooth finishmaking possible the initial formation of the blade to a good airfoilsection without particularly regarding the smoothness of the bladesurface. The coating herein provided is extremely thin, on the order of0.001 inch in thickness, smooth, and follows the contour of the surfaceto which it is applied. Second, the member is protected from corrosionunder deleterious conditions, such as exposure to salt-laden air andlubricating oils. Thirdly, the film is not wet by fluids such as water,oil, or air. The non-wettability of the siloxane coated blade results ina surprising increase in efiiciency of the turbine in which the bladesare employed. The coated members are more resistant to icing than metalsurface members and also are free from deposits formed by the buildingup upon the blade surface decomposition products of lubricating oilemployed in the engine. The non-wettability by air of the coated fiuiddirecting surfaces reduces bubbling and turbulence upon rapid movementof air passing through the engine in contact with the surface.

As a specific example from the method of the present invention,particularly applied to the coating of a compressor blade, such asillustrated in the drawings, the following data is presented:

Test blades about 1% inches in length and 1 /4 inches in width wereprepared from an electrolytic iron powder by pressing at about 15 tonsper square inch. The powder consisted of 4 parts by weight of anelectrolytic iron powder of a particle size corresponding to minus 100mesh and 1 part by weight of an electrolytic iron powder having a sizeof minus 325 mesh. The compact had a porosity of about 25% and washeated in contact with pure copper in an infiltration furnace in anatmosphere of purified dry cracked ammonia. The compact and copper wereraised to a temperature of about 1200 C. to melt the copper so that theporous compact was infiltrated. The materials were maintained atinfiltration temperature for 15 minutes and the composite body wascooled in the furnace. The body contained approximately 75% by weightiron and 25% by weight copper.

The infiltrated blade was next etched with a mixture of chromic andsulphuric acids containing about 188. grams per liter chromic acid and1.9 grams per liter sulphuric acid. Following the etching, the blade wascadmium plated in a conventional cadmium plating bath containing anaqueous solution of 23 grams per liter cadmium oxide and 86 grams perliter sodium cyanide. Soluble cadmium anodes were employed in theplating bath and the effective current density was 18 amperes per squarefoot. Following the cadmium plating step, the plated blade was dipped inby weight aqueous chromium acid solution to neutralize the alkali fromthe plating bath. The cadmium coated blade was next heated at atemperature of 150 to dryness and then placed within a vacuum chamberand evacuated to a pressure of 1 mm. mercury. The blade was maintainedunder vacuum until testing showed that all air was exhausted from theedge pores of the piece. This testing was carried out by clos ing theoutlet from the vacuum chamber to the pump and noting any pressure drop.If a pressure drop occurred, it indicated that the pores were notcompletely evacuated. As soon as a steady reading of 1 mm. mercury wasobtained, an organosiloxane coating resin containing 15% resin solids byweight dispersed in toluene was admitted to the vacuum chamber. Theresin contained dimethylsiloxane, monomethy'lsiloxane, andphenylmethylsiloxane structural units. Following the coating of theblade, the vacuum was released and the coated blade was dipped intoluene to remove the organosiloxane polymer from the blade surface.

Following removal from the toluene dipping bath, the blade was sprayedwith a resin dispersion containing 35% resin solids dispersed intoluene, the amount of polymer sprayed on the blade being sufficient toform a coating of approximately 0.001 inches in thickness upon ouring.The coated article was air dried for 3 hours at room temperature,pre-baked for 1 hour at C., and subjected to a final baking for twelvehours at 260 C. Under actual operating conditions, the blade prepared asabove described was found to possess amazing erosion and corrosionresistant properties, to adhere tenaciously to the blade surface, and topossess desirable surface smoothness.

Blades prepared as above described were also plated with zinc from azinc plating bath and with tin from a tin plating bath. A similar bladewas also coated with aluminum by means of a conventional hot diptreatment.

Each of the above blades coated with zinc, tin or aluminum was coatedwith organosiloxane polymer as above described. These test blades werealso found to possess the desirable characteristics of erosion andcorrosion resistance, nonwettability, coating adherence, and surfacesmoothness.

It will, of course, be understood that various details of constructionmay be varied through a wide range without departing from the principlesof this invention, and it is, therefore, not the purpose to limit thepatent granted hereon otherwise than necessitated by the scope of theappended claims.

I claim as my invention:

1. The method of coating an iron compact infiltrated with copper whichcomprises etching the surface of said article to remove copper to adepth of from 0.002 to 0.01 inch, depositing a receptive metal selectedfrom the group consisting of cadmium, zinc, tin and aluminum over theetched surface, applying a first layer of an organosiloxane polymer tothe receptive metal layer, subsequently applying a second layer of anorgano-siloxane polymer to said first layer without curing said firstlayer, the combined thickness of said first and second layers being lessthan 0.00 inch, and then heating the coated article to a temperature ofat least 230 C. to cure the layers and bond the coating to the articlethrough the formation of an interfacial receptive metal oxide firmlybonding said polymer to said metal by metal-oxygen linkages with saidpolymer.

2. A coated metal body of compacted iron particles infiltrated withcopper, said body having an iron surface substantially free from copper,a film of a receptive metal selected from the group consisting ofcadmium, zinc, tin and aluminum over the iron surface, a film oforgano-siloxane polymer over said receptive metal film, a film of ametal oxide of said receptive metal between said organo-siloxane polymerfilm and said receptive metal film, and an interfacial layer betweensaid organo-siloxane polymer film and said metal oxide film composed ofa reaction product of the receptive metal and the polymer and includingmetal-oxygen linkages with the polymer.

3. The method of forming a protective organosiloxane polymer coatingbonded by metaloxygen linkages to a non-receptive metal compact whichcomprises etching a porous iron compact infiltrated with copper toremove copper from the surface thereof and form an irregular surfacecomposed of iron particles, applying to said irregular surface a metalreceptive to said polymer and selected from the group consisting ofcadmium, zinc, tin and aluminum, limiting the thickness of said layer toprovide an irregular coating following the contour of the exposed ironparticles, coating an organosiloxane polymer onto said layer, removingthe polymer coating from the surface of the compact to leave a polymercoating only in the pores of the compact, applying a second coating ofthe organosiloxane polymer to form a continuous film of the desiredthickness on the compact, and heating the thus coated. compact to curethe polymer and form a smooth uncrazed surface bonded to the receptivemetal through metal-oxygen linkages.

4. The method of forming a smooth protective coating on a copperinfiltrated porous iron compact which comprises etching the compact toremove copper from the surface thereof and provide an irregular surfacecomposed of iron particles, applying a thin layer of a metal selectedfrom the group consisting of cadmium, zinc, tin and aluminum to theexposed iron particles, limiting the thickness of said layer to causethe layer to follow the uneven surfaces of said particles and provide anirregular covering layer, applying a layer of an organosiloxane resin tothe metal-coated irregular surface of the compact, and heating theorganosiloxane-coated compact to cure the resin and form an interfacialmetal oxide film including metal-oxygen linkages with the resin.

5. The method of coating a copper infiltrated iron compact with anorgano-siloxane resin which comprises etching the compact to removecopper from the surface and adjacent areas thereof, applying a metalreceptive to the resin and selected from the group consisting ofcadmium, zinc, tin and aluminum to the etched surface, evacuating thereceptive metal-coated compact to remove moisture and air from the poresthereof, applying a layer of an organosiloxane resin to the evacuatedcompact, removing the portions of said layer on the surface of thecompact without removing the layer from the walls of the pores of thecompact, applying a second layer of an organosiloxane resin to fill thepores and form a continuous film on the compact, and baking the thuscoated compact at temperatures between 230 to 320 C. to createmetal-oxygen linkages between the resin and the receptive metal.

6. The method of forming a non-wettable, smooth airfoil contour on anairflow-directing member composed of copper infiltrated iron particleswhich comprises etching the member to remove the copper from the surfaceof the member and create an irregular surface of exposed iron particles,applying a metal selected from the group consisting of cadmium, zinc,tin and aluminum to the exposed iron particles for form ing an irregularsurface following the contour of the particles, evacuating themetal-coated member to remove air and moisture from the pores thereof,applying a layer of an organosiloxane polymer to the evacuated member tofollow the contour of the metal coating, drying said polymer layer,covering the thus dried layer with a second layer of the organosiloxanepolymer to form a smooth continuous coating, drying the second layer,and baking the multi-coated member to temperatures of from 230 to 320 C.for a period of about 6 to 12 hours to thereby form a smooth finishresistant to salt-laden air and lubricating oils, and incapable of beingwet by water or oil, said surface being bonded to the metal coating bymetal-oxygen linkages.

'Z. The method of forming a protective organosiloxane polymer coatedinfiltrated powdered metal article composed of metal which is notreceptive to the polymer which comprises etching the infiltrant metalout of the surface area of the article to leave the powdered metalparticles exposed for forming an irregular surface, applying to saidexposed particles metal selected from the group consisting of cadmium,zinc, tin and aluminum to cover and follow the contour of the outerfaces of the particles without penetrating into the pores therebetween,covering the thus coated particles with an organosiloxane polymer whichalso extends into said pores, and heat curing the polymer to react thereceptive metal with the polymer whereby a protective coating is formedanchored in the pores and bonded to the receptive metal-coated outersurfaces of the powdered metal particles.

8. A fluid-directing member which comprises a copper infiltrated ironcompact having an irregular surface composed of iron particlessubstantially free from copper, a coating of a receptive metal on theexposed iron particles selected from the group consisting of cadmium,zinc, tin and aluminum, said coating following the irregular surface ofsaid iron particles and being anchored thereto, a film of anorganosiloxane polymer covering said receptive metal coating andproviding a smooth exterior surface on said compact, and an interfaciallayer between said organosiloxane polymer film and said receptive metalcoating composed of a reaction product of the receptive metal and thepolymer and includ ing metal-oxygen linkages with the polymer.

9. A turbine blade which comprises a copper infiltrated iron compact,said compact having an irregular surface composed of iron particles andbeing free from copper to a depth of from 0.002 to 0.01 inch, a thinfilm of a receptive metal selected from the group consisting of cadmium,zinc, tin and aluminum'bonded to said iron particles and covering theexposed surfaces thereof, said film being sufficiently thin to followthe irregular contour of the exposed iron particles and provide anirregular surface, a film of an organosiloxane polymer over thereceptive metal and following the irregularities thereof, saidorganosiloxane polymer film having a smooth exterior continuous surface,a metal oxide film between the polymer film and the receptive metal, andan interfacial layer between the organosiloxane polymer film and themetal oxide film composed of a reaction product of the re- 11 ceptivemetal and the polymer and including Number metal-oxygen linkages withthe polymer. 1,800,730 2,394,816 References Cited in the file of thispatent 2,459,013 UNITED STATES PATENTS 5 2,494,920 2,553,362 Number NameDate 776,518 Junggren Dec. 6, 1904 996,855 Hodgkinson July 4, 1911Number 1,608,694 Cain Nov. 30, 1926 10 432,33 1,651,278 Humphries Nov.29, 1927 Name Date Holzwarth Apr; 14, 1931 Soday Feb. 12, 1946 De Monteet a1 Jan. 11, 1949 Warrick Jan. 17, 1950 Dannenberg May 15, 1951FOREIGN PATENTS Country Date Great Britain July 25, 1935

1. THE METHOD OF COATING AN IRON COMPACT INFILTRATED WITH COPPER WHICHCOMPRISES ETCHING THE SURFACE OF SAID ARTICLE TO REMOVE COPPER TO ADEPTH OF FROM 0.002 TO 0.01 INCH, DEPOSITING A RECEPTIVE METAL SELECTEDFROM THE GROUP CONSISTING OF CADMIUM, ZINC, TIN AND ALUMINUM OVER THEETCHED SURFACE, APPLYING A FIRST LAYER OF AN
 2. A COATED METAL BODY OFCOMPACTED IRON PARTICLES INFILTRATED WITH COPPER, SAID BODY HAVING ANIRON SUFACE SUBSTANTIALLY FREE FROM COPPER, A FILM OF A RECEPTIVE METALSELECTED FROM THE GROUP CONSITING OF CADMIUM, ZINC, TIN AND ALUMINUMOVER THE IRON SURFACE, A FILM OF ORGANO-SILOXANE POLYMER OER SAIDRECEPTIVE METAL FILM, A FILM OF A METAL OXIDE OF SAID RECEPTIVE METALBETWEEN SAID ORGANO-SILOXANE POLYMER FILM AND CEPTIVE METAL FILM, AND ANINTERNAL LAYER BETWEEN SAID ORGANO-SILOXANE POLYMER FILM ACID SAID METALOXIDE FILM COMPOSED OF A REACTION PRODUCT OF THE RECEPTIVE METAL AND THEPOLYMER AND INCLUDING METAL-OXYGEN LINKAGES WITH THE POLYMER.